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Claims  |
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What is claimed is:
1. A two axis linear motor comprising:
a magnet structure having at least two high energy permanent magnets and an
elongated central pole piece and a pair of elongated side pole pieces
disposed parallel and adjacent to said central pole piece in the elongated
direction to create a pair of magnetic flux gaps with respect to said
central magnet pole piece,
an armature structure adapted to fit over and around said central pole
piece, said armature structure having a first coil winding means disposed
in a first coordinate reference plane in said pair of magnetic flux gaps
and a second coil winding means in a second and different coordinate
reference plane in said pair of magnetic flux gaps, and
a suspension flexure structure means for mounting said armature structure
to said magnet structure for movement in two directions, the first
direction perpendicular to said first coordinate reference plane and the
second direction perpendicular to said second reference plane, said
suspension flexure structure means supporting said armature structure
against undesired rotations and translations while allowing the first and
second movements with respect to said magnet structure.
2. The structure of claim 1 wherein said suspension flexure structure is a
pair of opposed parallelogram suspension flexures in which a first
parallelogram suspension flexure has two parallel wire elements supporting
one end of said armature from one side of said central pole piece and a
second parallelogram suspension flexure has two parallel wire elements
supporting the other end of said armature from the other side of said
central pole piece.
3. The structure of claim 1 wherein said armature structure first coil
winding means is a pair of tracking coil windings each having a first
portion disposed in said first coordinate reference plane in said magnetic
flux gaps and a second portion which returns in a different reference
plane outside the magnetic flux gaps.
4. The structure of claim 1 wherein the central pole piece of said magnet
structure has an aperture and said armature has a means for mounting an
objective lens over said aperture.
5. The structure of claim 1 wherein each of said elongated side pole pieces
is formed with a pair of faces projecting closer to the central pole piece
at the ends of the side pole piece and so that the ends of the armature
are within the narrower flux gap formed by said faces in conjunction with
said central pole piece so that the greatest moving force is exerted at
the ends of the armature to better control armature movement and to limit
undesired armature movement.
6. The structure of claim 1 wherein said armature structure is formed with
a pair of top mounting posts adapted for connection with said flexure
structure means and further comprising a cover structure adapted to
mechanically secure the linear motor and for connection with said central
pole piece, said cover structure including at least a pair of slot
elements adapted to conform to said armature mounting posts and to limit
the extreme limits of travel of said armature by means of said slots
disposed adjacent the path of travel of said mounting posts.
7. The suspension flexure structure means of claim 1 having a natural
frequency of vibration below 50 Hz.
8. A two axis linear motor comprising:
a lower magnetic pole piece forming a base structure,
a pair of side magnets mounted one on each side of said lower pole piece,
a pair of upper pole pieces mounted one on each side magnet,
an inner central pole piece mounted to said lower magnetic pole piece and
spaced apart from each of the upper pole pieces to form magnetic flux gaps
with the inner central pole piece and each upper pole piece,
an armature for carrying a lens assembly,
a first coil winding on said armature operative when current is passed
therethrough to generate focusing motion of said armature,
a second and third coil windings on said armature orthogonal to said first
coil winding operative when current is passed therethrough to generate
tracking motion of said armature,
mounting means for mounting said armature in to be disposed over and around
said central inner pole piece and position said first, second and third
coils the flux gaps between the upper side pole pieces and the central
inner pole pieces.
9. The linear motor of claim 8 wherein each of the upper side pole pieces
is formed with a pair of faces to be closer to the central inner pole
piece at the ends thereof so as to concentrate magnetic flux.
10. The linear motor of claim 8 wherein said linear motor has an aperture
for the passage of light through said inner pole piece and said armature
carries a lens assembly over said aperture.
11. The linear motor of claim 8 wherein said armature carries a flag in
relationship to a stationary portion of said motor and further comprising
a light assembly and a light detecting means disposed with respect to said
flag so that movement of said flag causes a variation of light received by
said light detecting means to monitor movement of said armature.
12. The structure of claim 8 wherein each of said elongated side pole
pieces is formed with a pair of faces projecting closer to the central
pole piece at the ends of the side pole piece and so that the ends of the
armature are within the narrower flux gap formed by said faces in
conjunction with said central pole piece so that the greatest moving force
is exerted at the ends of the armature to better control armature movement
and to limit undesired armature movement.
13. The structure of claim 8 wherein said armature structure is formed with
a pair of top mounting posts adapted for connection with said flexure
structure means and further comprising a cover structure adapted to
mechanically secure the linear motor and for connection with said central
pole piece, said cover structure including at least a pair of slot
elements adapted to conform to said armature mounting posts and to limit
the extreme limits of travel of said armature by means of said slots
disposed adjacent the path of travel of said mounting posts.
14. A linear motor for operation on two orthogonal axes, comprising:
a stationary magnet and pole piece structure for generating a magnetic
field between a pair of magnetic flux gaps, including a center inner
structure and a surrounding outer structure, having a pair of upper
elements one of which is disposed adjacent to each side of the inner
center piece and defining the magnetic flux gaps as part of a complete
magnetic circuit including the inner center piece and the outer structure,
an armature disposed around said inner center structure and within said
flux gaps,
a first coil means supported by said armature for causing movement in a
first direction,
a second coil means supported by said armature for causing movement in a
second direction orthogonal to the first direction,
said first and second coil means being supported by said armature within
said flux gaps formed by said stationary magnet and pole piece structure,
a flexure support means for said armature for supporting said armature
within said flux gaps for linear motion in said first and second
directions and for restraining other movements of said armature, said
flexure support means comprised of first and second support wires
extending from said stationary structure to one end of said armature and
forming a parallelogram structure orthogonal to said first and second
directions and third and fourth support wires extending from said
stationary structure to the other end of said armature and forming a
parallelogram structure orthogonal to said first and second directions.
15. The structure of claim 14 wherein said flexure support means is a pair
of opposed parallelogram suspension flexures in which a first
parallelogram suspension flexure has two parallel wire elements supporting
one end of said armature from one side of said central inner piece and a
second parallelogram suspension flexure has two parallel wire elements
supporting the other end of said armature from the other side of said
central inner piece.
16. The structure of claim 14 wherein said armature structure first coil
winding means is a pair of tracking coil windings each having a first
portion disposed in a first coordinate reference plane in said magnetic
flux gaps orthogonal to the tracking direction and a second portion which
is in a different reference plane outside the magnetic flux gaps.
17. The structure of claim 14 wherein the central inner piece of said
stationary magnet structure has an aperture and said armature has a means
for mounting an objective lens over said aperture.
18. The flexure support means of claim 14 having a natural frequency of
vibration below 50 Hz.
19. The structure of claim 14 wherein each of said elongated side pole
pieces is formed with a pair of faces projecting closer to the central
pole piece at the ends of the side pole piece and so that the ends of the
armature are within the narrower flux gap formed by said faces in
conjunction with said central pole piece so that the greatest moving force
is exerted at the ends of the armature to better control armature movement
and to limit undesired armature movement.
20. The structure of claim 14 wherein said armature structure is formed
with a pair of top mounting posts adapted for connection with said flexure
structure means and further comprising a cover structure adapted to
mechanically secure the linear motor and for connection with said central
pole piece, said cover structure including at least a pair of slot
elements adapted to conform to said armature mounting posts and to limit
the extreme limits of travel of said armature by means of said slots
disposed adjacent the path of travel of said mounting posts.
21. A two axis linear motor comprising:
a magnet structure having at least two high energy permanent magnets and an
inner pole piece means and a pair of side pole piece means disposed
adjacent to said inner pole piece means to create a pair of spaced-apart
magnetic flux gaps with respect to said inner pole piece means,
an armature structure adapted to fit over and around said inner pole piece
means, said armature structure having a first coil winding means disposed
in a first coordinate reference plane in said pair of magnetic flux gaps
and a second coil winding means in a second and different coordinate
reference plane in said pair of magnetic flux gaps, and
a suspension flexure structure means for mounting said armature structure
to said magnet structure for movement in two directions, the first
direction perpendicular to said first coordinate reference plane and the
second direction perpendicular to said second reference plane, said
suspension flexure structure means supporting said armature structure
against undesired rotations and translations while allowing the first and
second movements with respect to said magnet structure.
22. The structure of claim 21 wherein said suspension flexure structure is
a pair of opposed parallelogram suspension flexures in which a first
parallelogram suspension flexure has two parallel elements supporting one
end of said armature from one side of said inner pole piece means and a
second parallelogram suspension flexure has two parallel elements
supporting the other end of said armature from the other side of said
inner pole piece means.
23. The structure of claim 21 wherein said armature structure first coil
winding means is a pair of tracking coil windings each having a first
portion disposed in said first coordinate reference plane in said magnetic
flux gaps and a second portion which returns in a different reference
plane outside the magnetic flux gaps.
24. The structure of claim 21 wherein said inner pole piece means of said
magnet structure has an opening and said armature has a means for mounting
an objective lens over said opening.
25. The structure of claim 21 wherein each of said side pole pieces is
formed with a pair of faces projecting closer to the inner pole piece
means at the ends of said side pole piece means and so that the ends of
the armature are within the narrower flux gap formed by said faces in
conjunction with said inner pole piece means so that the greatest movement
force is exerted at the ends of the armature to better control armature
movement and to limit undesired armature movement.
26. The structure of claim 21 wherein said armature structure is formed
with a pair of top mounting posts adapted for connection with said flexure
structure means and further comprising a cover structure adapted to
mechanically secure the linear motor and for connection with said inner
pole piece means, said cover structure including at least a pair of slot
elements adapted to conform to said armature mounting posts and to limit
the extreme limits of travel of said armature by means of said slots
disposed adjacent the path of travel of said mounting posts.
27. The suspension flexure structure means of claim 21 having a natural
frequency of vibration below 50 Hz.
28. A linear motor for operation on two orthogonal axes, comprising:
a stationary magnet and pole piece structure for generating a magnetic
field between a pair of magnetic flux gaps, including an inner pole piece
means and a surrounding outer pole piece means, said structure defining a
pair of magnetic flux gaps, each flux gap being part of a complete
magnetic circuit including the inner pole piece means and the outer pole
piece means,
an armature disposed around said inner pole piece means and within said
magnetic flux gaps,
a first coil means supported by said armature for causing movement in a
first direction,
a second coil means supported by said armature for causing movement in a
second direction orthogonal to the first direction,
said first and second coil means being supported by said armature within
said flux gaps,
a flexure support means for said armature for supporting said armature
within said flux gaps for linear motion in said first and second
directions and for restraining other movements of said armature, said
flexure support means comprised of first and second support members
extending from said stationary structure to one end of said armature and
forming a parallelogram structure orthogonal to said first and second
directions and third and fourth support members extending from said
stationary structure to the other end of said armature and forming a
parallelogram structure orthogonal to said first and second directions.
29. The structure of claim 28 wherein said flexure support means is a pair
of opposed parallelogram suspension flexures in which a first
parallelogram suspension flexure has two parallel members supporting one
end of said armature from one side of said inner pole piece means and a
second parallelogram suspension flexure has two parallel members
supporting the other end of said armature from the other side of said
inner pole piece means.
30. The structure of claim 28 wherein said armature structure first coil
winding means is a pair of tracking coil windings each having a first
portion disposed in a first coordinate reference plane in said magnetic
flux gaps orthogonal to the tracking direction and a second portion which
is in a different reference plane outside the magnetic flux gaps.
31. The structure of claim 28 wherein the inner pole piece means of said
stationary magnet structure has an opening for light travel and said
armature has a means for mounting an objective lens over said opening.
32. The flexure support means of claim 28 having a natural frequency of
vibration below 50 Hz.
33. The structure of claim 28 wherein each of said side pole piece means is
formed with a pair of faces projecting closer to the inner pole piece
means at the ends of the side pole piece means so that the ends of the
armature are within the narrower flux gap formed by said faces in
conjunction with said inner pole piece means so that the greatest moving
force is exerted at the ends of the armature to better control armature
movement and to limit undesired armature movement.
34. The structure of claim 28 wherein said armature structure is formed
with a pair of top mounting posts adapted for connection with said flexure
structure means and further comprising a cover structure adapted to
mechanically secure the linear motor and for connection with said inner
pole piece means, said cover structure including at least a pair of slot
elements adapted to conform to said armature mounting posts and to limit
the extreme limits of travel of said armature by means of said slots
disposed adjacent the path of travel of said mounting posts. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a two axis linear motor for carrying the
objective lens in an optical head in an optical recording system of the
type in which a laser beam is used to record and play back information
optically from a rotating disk containing optical media.
It is well known in the art of the optical recording that an objective
lens, as carried by the optical head in an optical recording device, must
be moved continuously to focus the laser beam passing through an objective
lens to the optical media because of continuous variations in the distance
from the lens to the rotating disk as a result of mechanical wobble in the
drive system. Even a very slight amount of wobble in the disk will cause
the laser beam to be out of focus and, of course, correct focus is
critical to this recording technique. If the laser beam is not properly
focused, the beam power density will not be high enough to accomplish
writing on the media.
Optical heads are known of a type in which a voice coil structure moves an
armature in which an objective lens is mounted for movement towards and
away from the optical media disk. The optical head is carried by an arm
which provides for coarse position control. In addition, it is also known
that it is desirable to have a fine position control to move the objective
lens inwardly and outwardly in the radial direction with respect to the
disk in order to correct minor tracking errors for the particular
recording track on which it is desired to focus the objective lens. An
optical read device is known in which both focusing movement and inward
and outward tracking movement is achieved in the same device. This device
is described in European Patent Office Publication No. 0 002 547 published
on June 27, 1979. This publication shows separate coil winding and magnet
structure combinations for both the tracking movements and for the
focusing movements. When separate suspensions were used for tracking and
focus in previous designs, unacceptable mechnical coupling existed between
the two motions.
It is an object of the present invention to provide an improved two axis
linear motor for use in an optical recording head for carrying an
objective lens in an optical recording system.
SUMMARY OF THE INVENTION
The present invention is a two axis linear motor for carrying an objective
lens in an optical head for an optical recording system. The linear motor
of the present invention consists of a magnet structure which is
stationary with respect to the optical head structure and an armature body
structure, which moves with respect to the magnet structure, for carrying
the objective lens which focuses the laser beam on the optical media. The
magnet structure is elongated in the direction which will be the tracking
direction of the linear motor.
The stationary magnet structure consists of two side permanent magnets with
a central pole piece placed between the magnets. The central pole piece
forms a structure which also has an aperture through which the laser beam
may pass. The side magnets also have side pole pieces. The side magnets
and side pole pieces are placed on either side of and parallel to the
central pole piece structure to form two separate and complete magnetic
flux circuits in which the armature is located. The side pole pieces are
attached to each of the side permanent magnets and oriented with the same
magnetic polarity and elongated in the tracking direction. These parallel
side pole pieces form a pair of flux gaps with the central pole piece.
The armature is a structure which fits over the central pole piece and
rides in the magnetic flux gaps formed between the central pole piece and
the two side pole piece structures which are parallel and adjacent to the
central pole piece structure. This design is such that the magnetic flux
in the flux gaps is either running towards the central pole piece from
both side pole piece structures or the magnetic flux is running on both
sides from the central pole piece structure to the side pole piece
structures. In other words, in order for the armature coils to generate
the necessary motor movement, flux must either run towards the central
pole piece from the side pole pieces or away from the central pole piece
to the side pole pieces. However, with the coil winding structure of the
preferred embodiment of the invention, magnetic flux cannot be designed to
run to the central pole piece from one side and away from the other side
and have the motor generate the required movements.
The armature carried two different coil winding systems. The first coil
winding system consists of the focusing coil system which causes the
armature to move up and down carrying the objective lens up and down in a
coordinate system which brings the objective lens into and out of focus
with respect to the recording media. The other coil winding system is the
tracking winding system which causes the armature to move longitudinally
back and forth in the direction in which the magnet structure is
elongated. Both the tracking coils and the focusing coils function in the
same magnet structure and the same magnetic flux gap system formed between
the central pole piece structure and the two parallel side magnet and pole
piece structures. The magnet structures contain high energy magnets so
that comparatively high energy movements of the armature may occur using
the available drive current.
The armature is carried by a suspension flexure structure which is designed
to be extremely resistant to undesired motion and which is intended to be
comparatively free from unwanted harmonic vibration caused by either
outside disturbances which may occur in an optical recording system or by
the system itself in response to drive signals. The suspension system
provides for an essentially linear path of movement for the armature in
the tracking and in the focus directions for deflections of the magnitude
necessary to make the system operative. This characteristic is achieved
because the suspension system does not have mechanically fitted pivots or
other similar features which could produce mechanical variations in
motion. The geometry of the system is comparatively simple which allows
for a comparatively low mass in the system. Further, the mass distribution
of the system can be such that undesired resonant vibration of the system
is prevented both as a result of outside disturbances and as a result of
excitation of the coil winding systems.
In the figures:
FIG. 1 shows an exploded view of a two axis linear motor according to the
present invention in connection with use as an optical head in an optical
recording system.
FIG. 2 shows another embodiment of the two axis linear motor according to
the present invention.
FIG. 3 shows an exploded view of the embodiment of the two axis linear
motor according to the present invention as shown in FIG. 2.
FIG. 4 shows a detail of the linear motor of FIGS. 2 and 3.
FIG. 5 shows an exploded view of a further embodiment of the two axis
linear motor according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a two axis linear motor 10 according to the
present invention is shown. The linear motor 10 is comprised of a magnet
structure 12, generally, and an armature structure 14, generally, which
fits over and around at least a part of the magnet structure. The magnet
structure 12 forms a dual magnetic circuit by means of two permanent
magnets 24 and 26 acting through two upper pole pieces, 32 and 34, which
are of the same magnetic polarity, and a single lower pole piece 16 to
which is attached a central pole piece 20 which the armature structure 14
surrounds. A magnetic flux gap is defined between the central pole piece
20 and each of the upper pole pieces, 32 and 34, with magnetic flux lines
crossing these gaps in opposite directions, i.e. toward the central pole
piece on both sides or away from the central pole piece on both sides, as
indicated by the polarity markings and arrows in FIG. 1. This gap and the
field which its orientation prescribes are used for movement of the
armature 14 as will be explained.
The coordinate reference system on which this description is based is shown
at 22 in which the Z axis represents the focusing axis with respect to a
recording media, the X axis represents a radial tracking axis with respect
to moving from one recording track to another on the media while the Y
axis is tangential to a data track on the recording media.
The magnet structure 12 is elongated in the X axis direction which
represents the radial inward and outward track selection direction with
respect to the recording media. Pole piece 32 has an inward edge which
forms a parallel planar face adjacent to an edge 36 of pole piece 20. Pole
piece 34 has an inward edge 38 which forms an elongated planar gap with an
adjacent, outer facing edge of pole piece 20. The gap between pole piece
34 and pole piece 20 shall be referred to as flux gap 40 and the gap
between the central pole piece 20 and pole piece 32 shall be referred to
as flux gap 42.
The armature 14 has a body structure 44 having an aperture for mounting an
objective lens assembly 48 which fits over and around the central pole
piece 20. The objective lens assembly 48 is fixed over an aperture 50
which passes through pole piece 20 so that the laser beam of the optical
recording system can pass through to the objective lens assembly 48. The
armature body structure 44 carries a pair of tracking coil windings 52 and
54 relatively displaced towards either end thereof and which are connected
in series electrically.
Because of the pole piece 16, the tracking coil windings 52 and 54 cannot
go entirely around the armature body 44, in this embodiment of the
invention. Thus, each tracking coil winding must consist of a first
portion 56 and 58 associated with windings 52 and 54, respectively, which
cut the magnetic lines of flux in gaps 40 and 42 and a second portion 60
and 62 associated with coils 52 and 54, respectively, for completing the
electric circuit and which go around the ends of the armature body in the
X-Y plane and away from the magnetic flux gaps 40 and 42. The embodiment
of the invention shown in FIGS. 2, 3 and 5 have these coils going entirely
around the armature.
A single focus coil winding 64 passes completely around the armature body
44 in the X-Y plane to provide the focus motion of the linear motor. The
focus coil winding 64 is positioned so as to ride in magnetic flux gaps 40
and 42.
The armature body is supported by a pair of suspension flexures 66 and 68.
The suspension flexures are opposed parallelogram structures which
constrain the center of the armature structure 14 to move along a straight
line path in the X axis and in the Z axis, for small deflections and not
at all in the Y axis. The ends of the armatue may not move in a straight
line mode to the same extent as the center of the armature, but it is the
center of the armature where the lens is located which is critical. The
suspension flexures 66 and 68 provide restoring forces to return the
armature to the approximate center of its travel when no drive currents
are present in the tracking coil windings or the focus coil winding. As
the armature moves to the extremes of its travel, the radius from the
flexure attachment points remains constant, causing a very slight rotation
of the armature body 44 about the central Z axis.
Each suspension flexure has a magnet mounting piece 70 and 72 associated
with flexure 66 and flexure 68, respectively. The mounting piece 70 and
the mounting piece 72 may be fixed to the magnet structure by any
appropriate fastening means such as screws 74 and 76 which may pass
through the mounting piece 70 and into holes 78 and 80, respectively, in
magnet element 26.
The flexures 66 and 68 have flexure elements extending from the mounting
pieces 70 and 72 to the armature. In the particular application shown
herein, a pair of parallel wire elements 82 and 84 extend from mounting
piece 70 to be supported on the armature body 44. Similarly, flexure 68
has flexure parallel wire elements 86 and 88 extending from mounting piece
72 towards the armature body and which is fixed to the armature body.
These wire elements may be a wire or a spring wire such as music
instrument wire. These wire elements may also be used to carry driving
currents to the focus and tracking motor windings. The four wire elements,
as shown in this embodiment of the invention, 82, 84, 86 and 88 control
the movement of the armature body 44 allowing only X and Z translation of
the armature body with respect to the magnet structure. The structure
allows only extremely small rotations about the Z axis. One undesirable
movement is possible, a comparatively small amount of pitch (i.e. rotation
about the Y axis of the armature) in the longitudinal direction which is
seen in the X-Z plane. This X-Z plane pitch, however, is limited by the
comparatively small dimensions involved in the structure as well as the
stiffness of the wire elements 82, 84, 86 and 88.
By way of example, magnets 24 and 26 may be selected to be magnets 28 and
30 having extremely high energy, approximately 18 megagauss-oersted, in
the first embodiment. Eighteen megagauss-oersted is the energy product of
one type of magnet, and that product is achieved at one point of the
demagnetizing curve which represents an optimized operating condition for
that magnet, that is, the correct width of flux gap, length of magnet,
area and volume of magnet, flux concentration techniques, etc. That does
not necessarily mean that the magnet achieves that energy in any
particular application. This energy product is the maximum product of the
value of the magnetizing force and residual induction from the
demagnetizing curve of such a magnet. This value is indicative of the
energy that each cubic unit of magnet material can supply for external
use. In effect, this means that a coil with a given amount of current in
the force field of such a magnet can produce more energy than if a magnet
having a lower external energy were used. Magnets having this value of
external energy may be ceramic, rare earth, iron-cobalt magnets. Such
magnets are commercially available.
With reference to a particular embodiment according to FIG. 1, the armature
body 44 will typically move back and forth approximately 0.3 mm from a
central position in the tracking direction and approximately 0.7 mm up and
down from a central position in the focusing direction. Magnetic gaps 40
and 42 may be approximately 1 mm in width. The focusing coil may be
approximately 35 to 40 turns of No. 36 wire. Tracking coils 52 and 54 may
each be approximately 20 to 25 turns of No. 36 wire. The armature body 44
may be approximately 7 mm to 8 mm in width, the Y coordinate axis, and 16
mm to 18 mm in length, the X or tracking coordinate axis. The armature
body may weigh approximately 2 grams. The wires 82, 84, 86 and 88 may be a
music instrument wire and may be 303 stainless steel.
Referring now to FIGS. 2 and 3, which are assembled and exploded views,
respectively, of another embodiment of the invention, a linear motor
according to the present invention consists of a moving armature 100 and a
stationary magnet and pole piece assembly 102. The armature is a shell
structure which has an essentially hollow inner cavity. The armature is
supported by suspension wires 104, 106, 108, and 110. The armature has
mounting posts 105 and 109 to connect with and hold wires 104 and 108,
respectively. Similar mounting posts, not shown, are used for wires 106
and 110. Mounting posts 105 and 109 clamp the suspension wires firmly so
that they do not pivot or swivel at the post and so that movement is
controlled solely by bending of the wire. The armature has coils 112 and
114 corresponding to coils 52 and 54 in the embodiment shown in FIG. 1.
The armature has a focus coil 116 corresponding to coil 64 shown in the
embodiment of FIG. 1. The armature supports a lens assembly 118. The
details of the lens assembly are not critical to this application, but are
of course appropriate to the optical system for optical recording.
The stationary assembly has a lower pole piece 130 which forms a base for
the structure. Secured to the lower pole piece 130 is an inner pole piece
132 which is actually contained within the armature assembly and which
must be inserted into the armature assembly in order to wind coils 112 and
114. This inner pole piece 132 is secured to the lower pole piece 130
using screws 134. In assembling the inner pole piece 132 into the hollow
cavity of the armature 100, coil winding plates 101 and 103 are fitted
into the bottom of the armature to hold the pole piece 132 and to prevent
the armature from collapsing as the coils are wound. In this embodiment
the coils are wound after the foregoing mechanical assembly.
Mounted to the lower pole piece 130 are side magnets 140 and 142 which
function in much the same manner as the magnets described in connection
with the embodiment of FIG. 1.
Supported on top of magnets 140 and 142 are upper pole pieces 150 and 152
which have faces 154, 156, 158 and 160, respectively, for forming flux
gaps through the coils on the armature and to the inner pole piece 132.
Faces 154, 156, 158 and 160 project closer to the inner pole piece than
the rest of the respective upper pole pieces to form narrower flux gaps
for coils 112 and 114 and to concentrate the magnetuc flux at the ends of
the armature so that the greatest force is exerted at the ends of the
armature and not in the middle. By exerting moving forces at the ends of
the armature, better control of movement is achieved and less tendency to
undesired motion results.
The magnet and pole piece structures are held in place and supported by
front support 166 and rear support 168, respectively. It should be noted
that rear support 168 has a slot 170 formed therein. This is so that a
flag 172, which is carried by armature 100, may ride in the slot. The flag
has a very small slot 174 with an opening formed therein for the passage
of light. Light is projected by a light element 176 through slot 174 to a
photo transistor holder or light receiver 178. The operation of this
mechanism is to detect movement of the armature as indicated by the flag
moving slot 174 back and forth in the light beam created by the light
element 176.
This embodiment of the invention has the advantage over the embodiment
shown in FIG. 1 that coils 112 and 114 on the armature body pass entirely
around the armature body without having to take a detour around the end of
the armature body as shown in FIG. 1. However, this embodiment of the
invention does require that the inner pole piece 132 be permanently
captured by the coil structure and that the armature and inner pole piece
structure will be forever secured together. This embodiment may be most
desirable for most commercial applications of the present invention.
However, it is also possible that the embodiment of the invention shown in
FIG. 1 may also be seen to be desirable in some situations.
FIG. 4 is a detail of FIGS. 3 and 4 showing the light element 176
projecting light through slot 174 in flag 172 to a pair of light detectors
178a and 178b to determine flag motion. The difference in current produced
by detectors 178a and 178b is representative of changes in light intensity
caused by movement of flag 172. Thus, the differential current from the
detectors can be used to show the direction and amount of movement of the
armature.
Referring now to FIG. 5, another embodiment of the present invention is
shown. This embodiment is closely related to the embodiment shown in FIGS.
2, 3 and 4 and so therefore some of the parts or elements are identical.
In describing the embodiment of FIG. 5, identical parts and elements have
identical numbers as used in describing the embodiment of FIGS. 2, 3 and
4. Parts that are essentially similar and have essentially the same
function but with minor differences of structure use an element number
followed by a letter. Parts and elements that are totally different have
totally different numbers. The essential difference of the embodiment of
FIG. 5 from the other embodiments is in the mechanical packaging in which
an outer cover structure 200 is used to mechanically hold and secure the
other elements of the linear motor according to the present invention to a
base plate and lower magnetic pole piece element 130a. As shown in FIG. 5,
and a comparison may be made with FIG. 3 the lower pole piece and base
plate element 130a forms a similar function in assembling the linear motor
but has a different configuration for the embodiment of FIG. 5 so that it
may mate with the cover element 200.
The armature 100 of the present embodiment is essentially identical to the
armature of the embodiment as shown in FIG. 4. However, the mounting posts
105a and 109a are slightly different in order to secure the supporting
flexure elements 104a, 106a, 108a and 110a. As may best be seen in FIG. 3,
wire elements 104, 106, 108 and 110 have a curved end portion which is
used to secure the wire elements in the mounting posts 105 and 109. In the
embodiment of the invention shown in FIG. 5, the wire elements 104a, 106a,
108a and 110a are straight and are inserted into a hole which is made in
the mounting posts 105a, 109a and 111a. Wire element 106a fits into a
mounting post, also, not shown.
Inner pole piece 132a performs essentially the same function in the same
fashion as inner pole piece 130 as shown in FIG. 3. Inner pole piece 132a
as shown in FIG. 5 is formed in a slightly different fashion however for
mounting to base plate and pole piece 130a. Magnets 140 and 142 as well as
pole pieces 150 and 152 are identical to the pole pieces of the embodiment
shown in FIGS. 2, 3 and 4.
Cover 200 is mounted to lower base plate and pole piece 130a using screws
mounted through the sides of the cover and into the sides of plate 130a.
Magnets 140 and 142 and pole pieces 150 and 152 are assembled on top of
plate 130a. Flexure support elements 202 and 204 are mounted to pole
pieces 150 and 152 using screws as shown. Flexure support elements 202 and
204 support suspension wire elements 104a, 106a, 108a and 110a which in
turn, together, support armature 100. Terminal plate 206 is mounted to
plate 130a and serves as a termination for the wires from the coil
windings. When assembled, mounting posts 105a and 109a on armature 100
project into and ride back and forth in slots 105a and 109b in cover 200.
It is intended that the armature and the mounting posts do not touch cover
200 at the edges of these slots, but the slots provide a guide and a limit
to the extremes of travel of the armature in order to protect the
structure. This embodiment of the invention has the advantage that
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